Tandem rotor helicopter



May 15, 1951 Filed Feb. 5, 1948 2 Sheets-Sheet 1 FIG.

Patented May 15, 1951 TANDEM ROTOR HELICOPTER Frank N. Piasecki, Lansdowne, Pa., assignor, by

mesne assignments, to Piasecki Helicopter Corporation, Morton, Pa., a corporation of Pennsylvania Application February 5, 1948, Serial No. 6,482

3 Claims. 1

This invention relates to rotary wing aircraft of the type disclosed in my application filed December 16, 1946, Serial No. 716,494, and which matured as Patent No. 2,507,993.

The principal object of this invention is to provide a rotary wing aircraft having high performance characteristics without increasing the size of the machine to such an extent that its use will be limited to large landing areas.

Another object of this invention is to provide a rotary wing aircraft wherein the relationship of the rotor axes to the longitudinal axis of the aircraft and to the ground line as established by the landing gear arrangement is such that the lift vectors of the rotors will be working at their optimum positions for all attitudes of flight.

- A still further object of this invention is to provide a rotary wing aircraft having two longitudinally spaced rotors mounted in overlapping relationship and geared together in such phase relationship that the rotors may intermesh when flapping without danger of blade interference.

Another objectof this invention is to provide anew and improved drive system arrangement for tandem rotor helicopters. 7

Other objects and advantages will become apparent when the following description is read in conjunction with the drawings forming apart of this specification.

Figure 1 is an inboard profile view showing the general construction and arrangement of the functional parts of the preferred embodiment of my invention.

Figure 2 is a similar view of a modified form.

Referring more particularly to Figure 1 of the drawings wherein the preferred embodiment of my inventionisshown as comprising a fuselage generally indicated by number II having rotors l2 and [3 carried at either end of the fuselage. The attitude of the craft as shown in this figure is that assumed when in forward flight. The fuselage I l is supported on the ground by a landing gear I4. The forward portion of the fuselage ll forms a pilot and passenger or cargo compartment [5. The aft portion of the fuselage ll houses a suitable power plant [6, and extending upwardly above the aft portion of the fuselage H is a vertical airfoil or stabilizer fin l1 inside of which is housed the rear pylon structure and rear rotor driv shaft. Located directly under the two rotors l2 and I3 are transmissions l8 and I9.

The power plant I6 is cooled by a fan drawing air in through an opening 22 provided in the forward portion of the vertical fin ll.

A landing gear I4 is comprised of two main wheels 23 and a tail wheel 2%; is provided for alighting and ground handling purposes.

Forming an important part of this invention is the relationship existing between the rotor axes a-n and b--b and the axis of minimum drag 0- 0 of the craft and the ground reference line d-d, as established by the landing gear arrangement. The axis of minimum drag or longitudinal axis cc of the aircraft is parallel with the top surface 25 of the fuselage II and parallel to the air flow about the craft when it is in forward flight. In order to maintain forward flight it is necessary that the lift vectors of the rotors be tilted forwardly. It should be noted that this requirement of flight is obtained by the angular relationship existing between the rotor shafts 2t and 27 and the minimum drag axis cc of the aircraft or flight line. The arrangement eliminates the use of cyclic pitch normally required by other types of helicopters and permits the front rotor to be mounted in close proximity to the top of the fuselage without danger of the blades flapping downwardly against the top of the fuselage structure.

Maximum'performance in vertical flight or take-off is obtained when the rotative axes of the aircraft are vertical and no cyclic pitch is being used. This is obtained in the present invention by arranging the landing gear in such a manner that the axis a-a and 11-1) and rotor shafts 25 and 21 are perpendicular to the ground line. When the aircraft is sitting in this position it is tilted slightly upwardly so that there is an angular relationship existing between the longitudinal axis cc and the ground reference line 01-01. When the aircraft is in the most used attitude which is that of forward flight, the fuselage is level adding to the comfort of the occupants and presents the least frontal area to the airstream.

The drive system is comprised of an engine drive shaft with which is incorporated a free wheeling unit 2], a front transmission It, a rear transmission [9, rotor shafts 26 and 2? and a drive shaft 36 drivingly connecting the front and rear transmissions I8 and IS. The drive shaft 36 runs parallel to the top of the fuselage.

The rear transmission unit [9 is comprised of a power input shaft 28 and two power output shafts 29 and 30. Fixed on the shaft 28 for rotation therewith are two pinions 3! and 32. The pinions 3| and 32 meshing with and normally driving the gears 33 and 34 fixed on the shafts 29 and 30 respectively. The shaft 28 also acts to transmit power from one rotor to the other 3 when the rotors are overrunning the power plant as when in autorotation. Incorporated in the rear transmission unit with the drive shaft is a drive clutch 35.

By providing the transmission arrangement as has been described it is possible to eliminate the mid-gear case usually employed in tandem rotor drive systems, thus effecting a weight saving and making possible a'more compact drive system arrangement wherein the power plant may be carried further forward in the fuselage thus achieving a better mass distribution. By using the bevel gears throughout the: system, as shown,

it is possible to angularly displace the variousdrive shafts with one anotherto obtain the desired drive arrangement without employing misaligned universal joints, thus eliminating. destruc tive vibration and loss of power.

In Figure 2 there is shown a modified arrangement of a drive system for helicopters of the type referred to in the present invention. The particular advantage of this type of arrangement is that standard rightangle gear reducing unitsinaybe used, thus affecting a considerable saving in cost over the special type transmissions required in other helicopters.

This modified arrangement includes a power plant 40 a drive shaft 4| extending therefrom, a mid-reduction unit 42 and a rear drive shaft 43 and front drive shaft 44', front and rear rotor transmissions 45 and 46 from which extends the front and rear rotor shafts 41 and 48 respectively. The mid-reducing unit 42 is comprised of pulleys 49 and '50, and adriving belt The use of this mid-gear case permits a selection of pulleys to vary the drive ratio to allow the use of standard gear reducing units. Manual and overunning clutches 52 and. 53' are incorporated with the drive shaft. 4 l.

I claim:

1.. In combination, a, tandem rotor helicopter comprised of an elongated fuselage, a power plant in the aft portion of said fuselage, a pair of upwardly extending lift rotor shafts carried by and projecting above said fuselage andspaced longitudinally thereof, means for applying power to said shafts comprising gear reduction units mounted at the lower ends of said rotor shafts, a transmission shaft extending along the underside of the upper surface of said fuselage in parallel relationship thereto and connected to the gear reduction unit of the forward of said shafts, adrive shaft extending upwardly and rearwardly from said power plant and connected to the rear gear reduction unit and: connected to said transmission shaft, the aft portion of said fuselage ex-' tending upwardly to enclose the rear rotor shaft and to form a vertical stabilizing fin.

2. In tandem rotor helicopters, in combination, an elongated fuselage, a landing gear, a pair of upwardly extending rotor shafts carried by said fuselage and spaced longitudinally thereof, lift rotors mounted on the upper ends of. said shafts, the forward shaft being inclined forwardly with respect to the major portion of the upper surface of said fuselage and both of said shafts being inclined forwardly with respect to the longitudinal axis of said fuselage, and bein perpendicular to the ground reference line when the helicopter is at rest upon the ground, the rear shaft being of greater length than the forward shaft to place the plane of the aft rotor above that of the forwardrotonthe: aft portion of the fuselage extend-- ing upwardly to house and support the rear rotor shaft and being streamlined to provide a vertical.

stabilizer, a drive system comprising reduction gears located at the lower ends of the forward and aft rotor shafts, a power plant located in the aft portion of said fuselage, adrive shaft extending rearwardly and upwardly from said power plant and connected to the aft reduction gears, a second drive shaft drivingly'connected to the forward reduction gears and extending rearwardly therefrom, said second drive shaft being connected to and normally driven by the first drive shaft; an overrunning clutch interposed between the first drive-shaft and the power plant to permit power to be transmitted-from the second drive shaft to the first drive shaft when the helicopter is in auto-rotative flight;

3. The combination as set forth in claim 2 and wherein the gear reduction units and second drive shaft are mounted in the fuselage in a plane parallelv to and closely underlying the major portion of the upper surface of the fuselage.

FRANK N, 'PIAsEcKI.

REFERENCES CITED The following references are of record in the 

